CN114678254B - Sample injection system for chemical ionization and mass spectrometer based on sample injection system - Google Patents
Sample injection system for chemical ionization and mass spectrometer based on sample injection system Download PDFInfo
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- 239000007924 injection Substances 0.000 title claims abstract description 81
- 238000000451 chemical ionisation Methods 0.000 title claims abstract description 33
- 230000003197 catalytic effect Effects 0.000 claims abstract description 32
- 238000001514 detection method Methods 0.000 claims abstract description 29
- 239000012855 volatile organic compound Substances 0.000 claims abstract description 22
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims abstract description 16
- 238000010438 heat treatment Methods 0.000 claims abstract description 13
- 238000005070 sampling Methods 0.000 claims abstract description 13
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 12
- 229910002092 carbon dioxide Inorganic materials 0.000 claims abstract description 8
- 239000001569 carbon dioxide Substances 0.000 claims abstract description 8
- VUZPPFZMUPKLLV-UHFFFAOYSA-N methane;hydrate Chemical compound C.O VUZPPFZMUPKLLV-UHFFFAOYSA-N 0.000 claims abstract description 4
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- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 claims description 3
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- -1 Polytetrafluoroethylene Polymers 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J49/00—Particle spectrometers or separator tubes
- H01J49/02—Details
- H01J49/04—Arrangements for introducing or extracting samples to be analysed, e.g. vacuum locks; Arrangements for external adjustment of electron- or ion-optical components
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- H—ELECTRICITY
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- H01J49/02—Details
- H01J49/04—Arrangements for introducing or extracting samples to be analysed, e.g. vacuum locks; Arrangements for external adjustment of electron- or ion-optical components
- H01J49/0468—Arrangements for introducing or extracting samples to be analysed, e.g. vacuum locks; Arrangements for external adjustment of electron- or ion-optical components with means for heating or cooling the sample
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J49/00—Particle spectrometers or separator tubes
- H01J49/02—Details
- H01J49/10—Ion sources; Ion guns
- H01J49/14—Ion sources; Ion guns using particle bombardment, e.g. ionisation chambers
- H01J49/145—Ion sources; Ion guns using particle bombardment, e.g. ionisation chambers using chemical ionisation
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Abstract
The invention discloses a chemical ionization sample injection system and a mass spectrometer based on the sample injection system. A chemical ionization sampling system, comprising: the device comprises a sample injection pipeline, a pipeline heat preservation module, a catalytic module and a sample injection temperature control module. The sample injection pipeline is used for conveying the gas to be detected; the pipeline heat preservation module is used for heating and preserving heat of the sample injection pipeline; the catalytic module is divided into two branches, wherein one branch is used for catalyzing VOCs in the gas to be detected into carbon dioxide and water under the high-temperature condition, and the other branch is used for directly conveying the gas to be detected. According to the invention, the temperature I in the sample injection pipeline and the temperature II of the catalytic module are regulated by the sample injection temperature control module to be respectively in the corresponding temperature ranges, so that the influence of the instrument noise floor on the detection result is reduced, meanwhile, the catalytic module is in the same heating and heat preservation area, so that the influence of the temperature on the detection result can be avoided, the error of the final detection result is reduced, and the detection accuracy of the instrument is improved.
Description
Technical Field
The invention relates to a chemical ionization sample injection system and a mass spectrometer based on the sample injection system, in particular to a chemical ionization sample injection system and a mass spectrometer based on the chemical ionization sample injection system, belonging to the technical field of environmental monitoring.
Background
Along with the continuous acceleration of the industrialization process in China, a large amount of industrial raw materials are inevitably used in the production and manufacturing process, and a large amount of pollution gas is generated. These gases include SO 2 、NO x CO, VOCs (volatile organic compounds), and the like. Because of the improvement of national environmental standards, the monitoring and treatment of the polluted gas are of great concern.
Mass spectrometers are important instruments for analyzing gas components, and typically include a sample injection system, an ion source, a drift tube, and an analyzer. The gas is ionized in the drift tube and migrates under the action of the electric field, and each ion has a specific mobility, so that the substance corresponding to each ion is identified according to the mobility. The uniformity of the drift tube electric field is critical to the resolution of the gas composition. Because the temperature of the gas in the sample injection system is not fixed, the background noise of the instrument has a larger influence on the measurement result, and the temperature of the gas to be detected in the sample injection can also have an influence on the electric field, the air pressure and the gas molecular number density in the drift tube, thereby causing serious errors on the measurement result.
Disclosure of Invention
The invention provides a chemical ionization sample injection system and a mass spectrometer based on the sample injection system, which are used for solving the problem of larger measurement result errors of the existing mass spectrometer.
The invention is realized by adopting the following technical scheme: a chemical ionization sample injection system comprises a sample injection pipeline, a pipeline heat preservation module, a catalytic module, a sample injection temperature control module and a pressure control module.
The sample injection pipeline is used for conveying gas to be detected; the pipeline heat preservation module comprises a first heater and a first temperature control box, and the first heater is used for heating the sample injection pipeline; the temperature control box is used for preserving heat of the sample injection pipeline.
The catalytic module comprises a catalyst, a catalyst carrier, a second heater, a second temperature control box and two three-way electronic valves, wherein the catalyst is used for catalyzing VOCs in the gas to be detected into carbon dioxide and water under the high-temperature condition; the catalyst carrier is used for carrying the catalyst and improving the high temperature resistance of the catalytic module; the second heater is used for heating the catalytic module; the second temperature control box is used for preserving heat of the catalytic module; the two three-way electronic valves are used for dividing the catalytic module into two branches, and one branch is used for conveying the catalyzed gas to be detected; the other branch is used for directly conveying the gas to be tested.
The sample injection temperature control module comprises an acquisition unit and a judging unit; the acquisition unit is used for acquiring the first gas temperature of the output port of the sample injection pipeline and the second gas temperature of the catalytic module; the judging unit is used for judging whether the first gas temperature exceeds a preset first temperature range or not, and if so, the output temperature of the first heater is regulated until the first gas temperature is within the first temperature range; the judging unit is further used for judging whether the second gas temperature exceeds a preset second temperature range, and if so, adjusting the output temperature of the second heater until the second gas temperature is within the second temperature range.
The method for calculating the first temperature range comprises the following steps:
since pv=nrt, n=n/NA;
n= (PV/RT) NA is available;
resulting in a molecular number density N '=n/v=pna/RT, i.e. t=pna/RN';
wherein P is pressure, V is volume, NA is Avwhereglode constant, T is temperature, R is molar gas constant, N is ion number, and N is amount of substance.
According to the invention, the catalytic module is divided into two branches through the two three-way electronic valves, one branch catalyzes VOCs in the gas to be detected into water and carbon dioxide under the high-temperature condition to obtain the instrument noise floor signal, the other branch directly conveys the gas to be detected, the influence of the instrument noise floor on the detection result is reduced through the comparison of the two branches, meanwhile, the influence of temperature on the detection result can be avoided because the two branches are in the same heating and heat-preserving area, the error of the final detection result is reduced, and the detection accuracy of the instrument is improved.
As a further improvement of the above solution, the sample injection system further includes a pressure control module, where the pressure control module includes: a pressure sensor, a sample injection pump and a pressure controller; the pressure sensor is used for collecting the air pressure of the gas to be detected; the sample injection pump is used for pressurizing the gas to be detected; the pressure controller is used for adjusting the output pressure of the gas to be measured.
As a further improvement of the scheme, the sample injection pipeline is a PTFE pipe, and the inner wall of the PTFE pipe is smooth.
As a further improvement of the above solution, the sample injection system further includes a filter, which is in communication with the sample injection pipe, for removing the particulate component in the gas to be measured.
As a further improvement of the above, the catalyst is a platinized aluminum oxide catalyst.
As a further improvement of the above, the catalyst carrier is a stainless steel pipe.
A mass spectrometer of a chemical ionization-based sample injection system, comprising: the chemical ionization sample injection system, the ion reaction system, the ion detection system and the data processing system.
The ion reaction system is used for chemically ionizing the gas to be detected to generate sample ions and enabling the sample ions to migrate; the ion detection system is used for collecting ion signals of the sample ions; the data processing system is configured to analyze the ion signal.
As a further improvement of the above, the ion reaction system includes: an ion source and a drift tube; the ion source is used for providing chemically ionized reactive ions; the drift tube is used for generating a uniform electric field, guiding gas to be detected and the reaction ions to generate sample ions through chemical ionization, and the sample ions and the reaction ions migrate under the action of the electric field.
As a further improvement of the above, the ion detection system includes: a vacuum module, an electron multiplier and a quadrupole mass analyzer; the vacuum module comprises a mechanical pump, a first molecular pump and a second molecular pump, and the mechanical pump is used for providing first-level vacuum; the molecular pump is used for providing second-stage vacuum; the second molecular pump is used for providing third-stage vacuum; the electron multiplier is used for amplifying an ion signal of the sample ions; the quadrupole mass analyzer is configured to separate the sample ions and the reaction ions by a mass-to-charge ratio.
As a further improvement of the above, the data processing system includes: the device comprises a data acquisition module, a data analysis module and an instrument control module; the data acquisition module is used for acquiring real-time signals of the mass spectrometer, wherein the real-time signals comprise water vapor flow, air pressure in the drift tube, temperature of the catalytic module and voltages of a plurality of circuits; the data analysis module is used for calculating and analyzing the ion signals and the real-time signals and outputting VOCs concentration in the gas to be detected and instrument operation instructions; the instrument control module is used for controlling the operation of the mass spectrometer according to the instrument operation instruction.
Compared with the existing mass spectrometer, the sample injection system for chemical ionization and the mass spectrometer based on the sample injection system have the following beneficial effects:
1. the catalytic module is divided into two branches through the two three-way electronic valves, wherein one branch catalyzes VOCs in the gas to be detected into water and carbon dioxide under the high-temperature condition to obtain an instrument noise floor signal, the other branch directly conveys the gas to be detected, the influence of the instrument noise floor on a detection result is reduced through the comparison of the two branches, meanwhile, the influence of temperature on the detection result can be avoided because the two branches are in the same heating and heat-preserving area, the error of the final detection result is reduced, and the detection accuracy of the instrument is improved;
2. the pressure control module is used for adjusting the air pressure of the gas to be detected output by the sample injection system, so that the pressure at the outlet of the sample injection system of the mass spectrometer is consistent with the pressure of the drift tube, the pressure in the drift tube, an electric field and the density of gas molecules are prevented from changing, and the measurement accuracy is improved;
3. the sample injection pipeline with corrosion resistance, high temperature resistance and low viscosity is adopted, so that the adsorption quantity of VOCs in the sample injection process is reduced, the gas to be measured is ensured to directly enter the drift tube only through the smooth pipeline, the measurement error is reduced, and the measurement precision of the instrument is improved;
4. preheating and preserving heat of the gas to be detected, reducing the adsorption quantity of the gas to be detected in a sample injection system, improving the efficiency of the catalytic reaction, reducing the heat loss rate and reducing the detection cost of the gas to be detected;
5. the electric field of the drift tube is kept stable, so that ionized gas molecules to be measured uniformly migrate according to the mass-to-charge ratio, and are further captured by the ion detection system in sequence, and the measurement accuracy is improved.
Drawings
FIG. 1 is a schematic diagram of a chemical ionization sample injection system according to embodiment 1 of the present invention;
FIG. 2 is a schematic diagram of a mass spectrometer of the sample injection system based on chemical ionization according to embodiment 1 of the present invention;
FIG. 3 is a flowchart illustrating the steps performed by the pressure control system of FIG. 1 to regulate air pressure.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Example 1
Referring to fig. 1 and 2, fig. 1 is a schematic structural diagram of a chemical ionization sampling system according to the present embodiment; fig. 2 is a schematic structural diagram of a mass spectrometer of the sample injection system based on chemical ionization in this embodiment. The mass spectrometer based on the chemical ionization sampling system comprises a chemical ionization sampling system, an ion reaction system, an ion detection system and a data processing system.
The sample injection system for chemical ionization comprises: the device comprises a sample injection pipeline, a pipeline heat preservation module, a catalytic module, a sample injection temperature control module, a pressure control module and a filter.
The sample injection pipeline is a PTFE (Polytetrafluoroethylene) pipe, and the inner wall of the PTFE pipe is smooth and is used for conveying gas to be detected. The PTFE pipe has the characteristics of corrosion resistance, high temperature resistance and low viscosity, and has longer service life and lower cost compared with a common sample injection pipeline. The gas to be measured may contain corrosive gases, such as sulfur compounds H 2 S, and the like, so that the sample injection pipeline has better corrosion resistance; in order to reduce the adsorption of substances to be detected to the inner wall of the pipeline, the sample injection pipeline is usually subjected to heating treatment, the temperature is usually 50-100 ℃, and the primary sample injection pipeline has better high-temperature resistance; the inner wall of the sample injection pipeline needs to be smooth as much as possible, and the aim of reducing the adsorption of the object to be detected to the inner wall of the pipeline is also achieved.
The input port of the sample injection pipeline is communicated with the filter and is used for filtering the gas to be detected, removing granular components in the gas to be detected, reducing abrasion of the gas to be detected on the inner wall of the sample injection pipeline and avoiding influence of the granular components in the gas to be detected on gas analysis. The filter can be an activated carbon filter or an electrostatic dust removal filter.
The pipeline heat preservation module comprises a first heater and a first temperature control box, and the first heater is used for heating the sample injection pipeline; the temperature control box is used for preserving heat of the sample injection pipeline. The temperature control box comprises a shell and an insulating layer, wherein the shell is fixed on the outer side of the sample injection pipeline and is used for accommodating the first heater; the heater I adopts a non-contact infrared heater, can directly heat the gas to be measured in the sample injection pipeline, avoids the gas to be measured from adhering to the heater I, and reduces measurement errors. The heat preservation layer can be made of glass wool material, has the characteristics of good formability, small volume density, low heat conductivity and the like, and has extremely high corrosion resistance; the heat insulating layer can also be a composite silicate material, and has the advantages of low heat conductivity coefficient, excellent heat insulating performance and low volume weight in the heat insulating material at a high temperature.
The catalytic module comprises a catalyst, a catalyst carrier, a second heater, a second temperature control box and two three-way electronic valves, wherein the catalyst is used for catalyzing VOCs in the gas to be detected into carbon dioxide and water at high temperature; the catalyst carrier is used for carrying a catalyst and improving the high temperature resistance of the catalytic module; the second heater is used for heating the catalytic module; the second temperature control box is used for preserving the temperature of the catalytic module; the two three-way electronic valves are used for dividing the catalytic module into two branches, and one branch is used for conveying the catalyzed gas to be detected; the other branch is used for directly conveying the gas to be measured. The catalyst is a platinized aluminum oxide catalyst, and has high activity and good catalytic effect. The catalyst carrier is a stainless steel pipeline, and the catalyst is uniformly arranged in the stainless steel pipeline in a fluff-like shape. The stainless steel has the characteristics of stable structure and high temperature resistance, and the catalyst is arranged in a fluff shape, so that the contact area of the catalyst with the gas to be detected can be increased, and the catalytic effect is improved. The heater II adopts a non-contact heater, such as an infrared heater, so that part of gas to be measured is prevented from adhering to the heater II, and the accuracy of instrument measurement is improved. One of the two branches catalyzes VOCs in the gas to be detected into water and carbon dioxide under the high-temperature condition to obtain an instrument noise floor signal, the other branch directly conveys the gas to be detected, the influence of the instrument noise floor on a detection result is reduced through the comparison of the two branches, meanwhile, the two branches are in the same heating and heat-preserving area, the temperature of the two branches can be kept the same, the influence of temperature difference on the detection result is avoided, the error of the final detection result is reduced, and the detection accuracy of the instrument is improved.
The pressure control module comprises a pressure sensor, a sample injection pump and a pressure controller; the pressure sensor is used for collecting the air pressure of the gas to be detected; the sample injection pump is used for pressurizing the gas to be detected; the pressure controller is used for adjusting the output pressure of the gas to be measured. The pressure sensor can adopt a non-contact type air pressure sensor, so that the adsorption of VOCs in the gas to be detected can be avoided, and the air pressure of the gas to be detected can be kept stable when the gas to be detected is conveyed to the drift tube. The pressure controller adjusts the output power of the sample injection pump according to the air pressure in the drift tube acquired in real time, and then adjusts the output air pressure of the gas to be measured.
The sample injection temperature control module comprises an acquisition unit and a judging unit; the acquisition unit is used for acquiring the first gas temperature of the output port of the sample injection pipeline and the second gas temperature of the catalytic module; the judging unit is used for judging whether the first gas temperature exceeds a preset first temperature range or not, and if so, the output temperature of the first heater is regulated until the first gas temperature is within the first temperature range; the judging unit is also used for judging whether the second gas temperature exceeds a preset second temperature range, and if so, the output temperature of the second heater is regulated until the second gas temperature is within the second temperature range.
The preset temperature range one can be calculated by the following formula:
since pv=nrt, n=n/NA;
obtainable n= (PV/RT) NA;
resulting in a molecular number density N '=n/v=pna/RT, i.e. t=pna/RN';
wherein P is pressure, V is volume, NA is Avwhereglode constant, T is temperature, R is molar gas constant, N is ion number, and N is amount of substance.
From the above formula, the temperature fluctuation affects the molecular number density in the drift tube, and thus affects the measurement result of the instrument, so that the control requirement on the temperature is very strict. The temperature in the sample injection pipeline is kept constant, the influence of the temperature of the gas to be measured on the molecular number density in the drift tube is reduced, and the measuring accuracy of the instrument can be effectively improved.
In this embodiment, the gas to be measured enters the sample injection pipeline after the particulate components in the gas to be measured are removed through the filter, the inner wall of the sample injection pipeline is smooth, and the pipeline heat preservation module is used for heating and preserving heat, so that the gas in the pipeline is in a constant temperature range, the adhesion of VOCs in the gas to be measured is reduced, and the influence of the instrument noise floor on the detection of the gas to be measured is reduced. The gas to be detected in the sample injection pipeline is divided into two branches, and the two branches are heated and insulated simultaneously through a heater II and a temperature control box II, so that the temperature of the two branches is kept the same. One branch adopts a catalyst to catalyze VOCs in the gas to be detected to generate water and carbon dioxide, so that a background signal of the instrument is obtained, the other branch is used for comparison, the influence of temperature on a measurement result is reduced, and the measurement accuracy of the instrument is improved.
The ion reaction system comprises an ion source and a drift tube. The ion source is used for providing chemically ionized reactive ions; the drift tube is used for generating a uniform electric field and guiding the gas to be detected and the reaction ions to generate sample ions through chemical ionization, and the sample ions and the reaction ions migrate under the action of the electric field. In-source H 2 O steam generates high-concentration H through glow discharge 3 O + And enters the drift tube under the action of a guiding electric field. The ion source and the drift tube are composed of a series of stainless steel ring electrodes, the adjacent electrodes are sealed by 0 circles of fluororubber, and the air pressure in the drift tube is generally 200-300Pa. The adjacent electrodes of the drift tube are connected with resistors with the same resistance, direct current voltage is applied to the electrodes at two ends of the drift tube, a uniform electric field can be formed in the drift tube, and the electric field mainly has two functions: (1) guiding the reaction ions and the product ions to pass through the drift tube; (2) providing collision energy and reducing the formation of cluster ions. The reaction ion passes through the sample injection electrode under the action of the guiding electric fieldThe small holes enter the drift tube, when the gas to be detected enters the drift tube through the sample inlet, molecular ion reaction can occur between the gas to be detected and the reaction ions in the drift tube, neutral gas molecules to be detected are ionized, and product ions and residual reaction ions enter the ion detection system under the action of an external electric field.
In this example, ionization of the sample is achieved by ion-molecule reactions. Reactive ions H entering into the drift tube 3 O + Chemical ionization with volatile organic compounds M occurs during downstream movement:
where k is the reaction rate constant. Number density of reagent ions in drift tube [ H ] 3 O + ]The time-dependent relationship is:
in the formula, [ H ] 3 O + ]And [ M ]]Respectively H in drift tube 3 O + And the number density of the volatile organic compounds M, t is the ion reaction time. Integration of equation (2.2) yields:
[H 3 O + ]＝[H 3 O + ] 0 exp(-k[M]t) (2.3)
wherein [ H ] 3 O + ] 0 H when no analyte gas is added 3 O + Is a number density of (a). At the end of the drift tube, product ions MH + The number density of (2) should be:
[MH + ]＝[H 3 O + ] 0 -[H 3 O + ] 0 exp(-kMt) (2.4)
＝[H 3 O + ] 0 [1-exp(-k[M]t)] (2.5)
under typical experimental conditions (pressure in the drift tube is 200Pa, temperature 25 ℃, voltage across the drift tube is 800V), the number density of gas molecules in the drift tube is about5×10 16 cm -3 Number density of 1ppm trace volatile organic compound [ M ]]Is 5 multiplied by 10 10 cm -3 The reaction time in the drift tube was about 9×10 -5 s, reaction rate constant is 2×10 -9 cm 3 K [ M ] at/s]t＝0.009<<1, there is therefore the following according to the majulin expansion:
exp(-k[M]t)≈1-k[M]t (2.6)
when the concentration of the volatile organic compound M in the gas is small, the number density of the reaction ions [ H ] before and after the reaction 3 O + ]The change is small and can be considered as a constant, namely:
[H 3 O + ]＝[H 3 O + ] 0 (2.7)
number density of product ions at the end of drift tube [ MH + ]The method comprises the following steps:
[MH + ]＝[H 3 O + ][M]kt (2.8)
because of ion signal I detected by mass spectrometer H3O+ And I MH+ Proportional to the number density of ions in the drift tube H 3 O + ]And [ MH ] + ]Therefore, the number density of trace volatile organic compounds M in the drift tube is:
where t is the ion reaction time, which is equal to the time for ions to migrate in the drift tube.
During the experiment, the pressure P in the drift tube P Can accurately measure by a vacuum gauge to give the number density [ N ] of molecules in the drift tube]The method comprises the following steps:
wherein R is 1 Is constant, T P Is the temperature within the drift tube.
From equations (2.17) and (2.18), the organic matter [ M ] to be measured in the drift tube can be calculated] ppb Is divided into (1)Pressure concentration (ppb):
since all the gas inside the drift tube comes from the outside atmosphere, the partial pressure concentration [ M ] of the organic matter M] ppb The partial pressure concentration of M measured by the mass spectrometer is the concentration of the gas to be measured before entering the drift tube, and the partial pressure concentration is the characteristic that the intrinsic spectrometer can realize quantitative detection.
The ion detection system comprises a vacuum module, an electron multiplier and a quadrupole mass analyzer. The vacuum module comprises a mechanical pump, a first molecular pump and a second molecular pump, and the mechanical pump is used for providing first-level vacuum; the molecular pump is used for providing second-stage vacuum; the second molecular pump is used for providing third-stage vacuum; the electron multiplier is used for amplifying ion signals of sample ions; the quadrupole mass analyzer is used for separating sample ions and reaction ions according to the mass-to-charge ratio. The ultimate vacuum of the mechanical pump may reach 10Pa or even lower, which constitutes the primary vacuum. The downstream outlet of the drift tube does not directly enter the mass spectrometer cavity in which the quadrupole mass analyzer is located, but passes through a transition region, which is a transition cavity that houses an ion lens system that directs ions. The ion lens consists of three electrodes, different direct current voltages are respectively connected to the three electrodes, and after ions enter the transition cavity from the drift tube, the ions smoothly enter the cavity area of the mass spectrometer under the action of the ion lens. The transition cavity is maintained in vacuum by a molecular pump, and the air pressure of the transition cavity is usually 10 when the instrument works normally -3 Pa, the transition chamber constitutes a second level of vacuum. Downstream of the transition chamber is a mass spectrometer chamber, which is the region where the mass analyzer quadrupole and detector electron multiplier are located. The mass spectrometer cavity is maintained under vacuum by a molecular pump, and the gas pressure is typically 10% when the instrument is in operation -4 The Pa magnitude, the mass spectrometer cavity constitutes a third level of vacuum.
The data processing system includes: the device comprises a data acquisition module, a data analysis module and an instrument control module; the data acquisition module is used for acquiring real-time signals of the mass spectrometerThe device comprises a water vapor flow, air pressure in a drift tube, temperature of a catalytic module and voltage of a plurality of circuits; the data analysis module is used for calculating and analyzing the ion signals and the real-time signals and outputting VOCs concentration in the gas to be detected and an instrument operation instruction; the instrument control module is used for controlling the operation of the mass spectrometer according to the instrument operation instruction. The mass spectrometer based on the chemical ionization sample injection system has the advantages that the data acquisition, the processing, the analysis and the like of the mass spectrometer are completed by control software, the control software can control the instruments such as the water vapor flow, the drift tube pressure, the catalytic temperature, the multipath voltage, the mass spectrometer, the GPS and the gas image sensor, the data acquisition, the concentration statistics, the data analysis and the like of all the instruments can be performed, and the concentration of VOC is displayed on an electronic map in real time. In addition, the self-protection function of the mass spectrometer and the molecular pump is introduced into the control software. The control software monitors the air pressure in the mass spectrometer in real time, controls the working state of the ion detection system according to the air pressure, automatically cuts off the power supply of the mass spectrometer when the air pressure is higher than a set warning value, and protects the quadrupole mass analyzer and the electron multiplier, wherein the warning value is 6.6x10 in general -4 Pa. When the air pressure continues to rise and exceeds a second warning value, the control software can automatically cut off the power supply of the vacuum pump set to protect the vacuum pump set, and the second warning value is l multiplied by 10Pa, so that the self-protection function of the mass spectrometer system is realized. The control software is more convenient and simpler to control the instrument, so that the efficiency and reliability of the whole control system are greatly improved.
Example 2
The mass spectrometer of the sample injection system based on chemical ionization can also be used for environmental monitoring and tracing the source travel car. The environment monitoring traceable navigation vehicle is called a walking air monitoring station, and the roof is provided with equipment such as an atmospheric particulate monitoring laser radar, an atmospheric particulate sampler and the like. When the navigation vehicle runs, the device can emit laser to the area to be monitored, and the laser radar collects echo signals scattered by the particulate matters in the air and analyzes the condition of the particulate matters in the atmosphere of the area in real time. The navigation vehicle can also perform three-dimensional and omnibearing three-dimensional monitoring on atmospheric pollutants, accurately position pollution sources in sensitive zones such as industrial parks and residential living areas, evaluate the concentration distribution condition of particles in the range of the areas, realize walking and measuring, locking the pollution areas and analyzing the pollution sources, and provide powerful technical support for preventing and treating the atmospheric pollutants.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.
Claims (10)
1. A chemical ionization sampling system, comprising:
the sample injection pipeline is used for conveying the gas to be detected;
the sample injection system is characterized by further comprising:
a pipe insulation module, comprising: a first heater and a first temperature control box; the heater is used for heating the sample injection pipeline; the temperature control box is used for preserving the temperature of the sample injection pipeline;
a catalytic module, comprising:
a catalyst for catalyzing VOCs in the gas to be measured into carbon dioxide and water under high temperature conditions;
the catalyst carrier is used for carrying the catalyst and improving the high temperature resistance of the catalytic module;
a second heater for heating the catalytic module;
a second control Wen Hezi for maintaining the temperature of the catalytic module; and
the two three-way electronic valves are used for dividing the catalytic module into two branches, and one branch is used for conveying the catalyzed gas to be tested; the other branch is used for directly conveying the gas to be detected; and
sample introduction temperature control module, it includes:
the acquisition unit is used for acquiring the first gas temperature of the output port of the sample injection pipeline and the second gas temperature of the catalytic module; and
a judging unit for judging whether the first gas temperature exceeds a preset first temperature range, if so, adjusting the output temperature of the first heater until the first gas temperature is within the first temperature range;
the judging unit is further used for judging whether the second gas temperature exceeds a second preset temperature range, and if so, adjusting the output temperature of the second heater until the second gas temperature is within the second temperature range;
the method for calculating the first temperature range comprises the following steps:
since pv=nrt, n=n/NA;
n= (PV/RT) NA is available;
resulting in a molecular number density N '=n/v=pna/RT, i.e. t=pna/RN';
wherein P is pressure, V is volume, NA is Avwhereglode constant, T is temperature, R is molar gas constant, N is ion number, and N is amount of substance.
2. The chemical ionization sampling system of claim 1, further comprising a pressure control module, said pressure control module comprising:
a pressure sensor for collecting the gas pressure of the gas to be measured;
the sample injection pump is used for pressurizing the gas to be detected; and
and the pressure controller is used for adjusting the output pressure of the gas to be measured.
3. The chemical ionization sampling system of claim 1, wherein the sampling tube is a PTFE tube with a smooth inner wall.
4. A chemical ionization sampling system according to claim 1, further comprising a filter in communication with said sampling conduit for removing particulate components from said gas under test.
5. The chemical ionization sampling system of claim 1 wherein said catalyst is a platinized aluminum oxide catalyst.
6. The chemical ionization sampling system of claim 1, wherein the catalyst support is a stainless steel tube.
7. A mass spectrometer of a chemical ionization based sample injection system, comprising:
the chemical ionization sampling system of claims 1-6;
an ion reaction system for chemically ionizing a gas to be measured to generate sample ions and for moving the sample ions;
an ion detection system for acquiring ion signals of the sample ions; and
a data processing system for analyzing the ion signal.
8. The mass spectrometer of claim 7, wherein the ion reaction system comprises:
an ion source for providing chemically ionized reactive ions; and
and the drift tube is used for generating a uniform electric field, guiding the gas to be detected and the reaction ions to generate sample ions through chemical ionization, and enabling the sample ions and the reaction ions to migrate under the action of the electric field.
9. The mass spectrometer of claim 7, wherein the ion detection system comprises:
the vacuum module comprises a mechanical pump, a first molecular pump and a second molecular pump, wherein the mechanical pump is used for providing first-level vacuum; the molecular pump is used for providing second-stage vacuum; the second molecular pump is used for providing third-stage vacuum;
an electron multiplier for amplifying an ion signal of the sample ions; and
a quadrupole mass analyzer for separating the sample ions and the reaction ions by a mass-to-charge ratio.
10. The mass spectrometer of claim 7, wherein the data processing system comprises:
a data acquisition module for acquiring real-time signals of the mass spectrometer, the real-time signals comprising: the flow rate of water vapor, the air pressure in the drift tube, the temperature of the catalytic module and the voltage of a plurality of circuits;
the data analysis module is used for calculating and analyzing the ion signals and the real-time signals and outputting VOCs concentration in the gas to be detected and instrument operation instructions;
and the instrument control module is used for controlling the operation of the mass spectrometer according to the instrument operation instruction.
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